Theresa May is coming under increasing pressure to publish the government’s legal advice on a possible Brexit deal.

The prime minister is facing calls to make public the guidance given to her by Attorney General Geoffrey Cox QC.

As Mrs May works to achieve a breakthrough in negotiations with the EU – currently still deadlocked on the Irish border issue – a growing number of MPs are demanding to see the legal assessment of any agreement before parliament votes on it.

Sky News understands Environment Secretary Michael Gove, a leading Brexiteer, is among those wanting to view Mr Cox’s advice in full before agreeing to a deal.

Up to eight cabinet ministers are reported to share Mr Gove’s position.

It comes after a cabinet discussion on Tuesday as to how the UK can ensure it is not placed permanently in a backstop arrangement, which is aimed at avoiding a hard border on the island of Ireland.

Tory Brexiteers are wary of a risk the UK could be left in an effective customs union with the EU after departing the bloc, curtailing the country’s ability to sign independent trade deals.

Veteran Conservative eurosceptic Sir Bill Cash is among Leave supporters wanting the legal advice to be made available.

He compared the publication of legal advice on a Brexit deal to the assessment of the legality of the 2003 invasion of Iraq.

He posted on Twitter: “The Attorney General’s advice on critical constitutional issues is for parliament and the country, not just for the government.

“As shadow attorney general I successfully pressured [Tony] Blair and the Attorney General to produce legal advice on the Iraq war and it should happen again.”

Former Brexit secretary David Davis used a newspaper article at the weekend to draw the same comparison between legal advice on a Brexit deal and the Iraq war.

The DUP, which props up the Conservative government at Westminster, also supports the publication of Mr Cox’s assessment of a Brexit agreement.

“If the House of Commons is going to have a meaningful vote on a deal that includes, and upon which this legal advice is very, very important, then I think people are entitled to know what that advice is.”

Image:MPs want to see the assessment of Attorney General Geoffrey Cox

Opposition parties also piled pressure on Mrs May to publish legal advice before MPs are asked to vote on an EU divorce deal.

“It must be a robust and credible proposal that guarantees there will be no return to a hard border in Northern Ireland after Brexit.

“That’s why it’s essential MPs are given the opportunity to scrutinise the Attorney General’s legal advice before voting on the final deal.”

Liberal Democrat Brexit spokesperson Tom Brake called on the government to “stop these murky games and publish their legal advice in full”.

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However, others urged caution, with Jacob Rees-Mogg – chair of the European Research Group of Conservative eurosceptics – telling Sky News: “It is essentially a political not a legal issue and I think the legal advice could easily become a distraction.”

Asked earlier this week if the government would publish the advice, Mrs May’s official spokesman pointed to a “long-standing principle that governments don’t comment on legal advice”.